Secondary batteries and fuel cells are used for powering or as auxiliary power units of hybrid cars, electric vehicles, and fuel-cell electric vehicles. Those batteries have disadvantages that the terminal voltage and the electrical capacitance are reduced at a low temperature and the electrolyte is decomposed at a high temperature to produce gas to increase the internal pressure, resulting in shortened battery life.
Some methods have been proposed for maintaining the power supply under proper temperature conditions. Laid-open Japanese Utility Model Registration Application No. 02(1990)-33492 (Patent Document 1) has disclosed a heat radiator for a battery-powered electronic device. The heat radiator for a battery-powered electronic device includes a heat transferring portion for transferring heat radiated from a heat producing portion to a battery and a shape-memory member placed between the heat transferring portion and the battery. The shape-memory member is displaced to separate the battery from the heat transferring portion at a predetermined transformation temperature or higher and to bring the battery into contact with the heat transferring portion at a temperature lower than the transformation temperature.
With this configuration, the battery can be activated by the heat transferred from the heat producing portion at a temperature lower than the transformation temperature. On the other hand, at a temperature higher than the transformation temperature, the heat transfer from the heat producing portion can be blocked to prevent deterioration of battery properties due to overheating.
Another prior art is Japanese Patent Laid-Open No. 2002-124224 (Patent Document 2) which has disclosed a battery pack including a metal heat radiator. The battery pack includes a heat-sensitive deformable element placed fixedly on a side of a battery case. If the temperature of the battery rises to exceed a predetermined level, the heat-sensitive deformable element is deformed and brought into contact with the metal heat radiator.
Since the heat-sensitive deformable element can be kept from contact with the metal heat radiator at a temperature equal to or lower than the predetermined level, the heat of the overheated metal heat radiator can be prevented from being transferred to the battery.
[Patent Document 1] Laid-open Japanese Utility Model Registration Application No. 02 (1990)-33492
[Patent Document 2] Japanese Patent Laid-Open No. 2002-124244